Anti-Glare Coatings with Aqueous Particle Dispersions and Methods for Forming the Same

ABSTRACT

Embodiments provided herein describe optical coatings, panels having optical coatings thereon, and methods for forming optical coatings and panels. A substrate is provided. A coating formulation is applied to the substrate. The coating formulation includes an aqueous-based suspension of particles. The particles have a sheet-like morphology and a thickness of less than about 100 nanometers (nm). The coating formulation is cured to form an anti-glare coating above the substrate. The anti-glare coating has a thickness of between 1 micrometer (μm) and 100 μm.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application No. 61/777,995, filed Mar. 12, 2013, entitled “Sol-Gel Coatings,” which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to optical coatings. More particularly, this invention relates to optical coatings that improve, for example, the anti-glare performance of transparent substrates and methods for forming such optical coatings.

BACKGROUND OF THE INVENTION

Anti-glare coatings, and anti-glare panels in general, are desirable in many applications including, portrait glass, privacy glass, and display screen manufacturing. Such optical coatings scatter specular reflections into a wide viewing cone to diffuse glare and reflection.

Most existing formulations (i.e., wet processing) used to form anti-glare coatings utilize toxic and environmentally unfriendly chemicals, such as polymer resins (e.g., urethanes, acrylates, methacrylates, epoxies, etc.) and/or volatile organic compound (VOC) solvents (e.g., xylene, alcohols, chlorocarbons, etc.), leading to increased costs due to material handling and Environmental, Health, and Safety (EHS) requirements.

Additionally, conventional anti-glare coatings produced by wet deposition methods offer very limited thermal processing options, requiring only low (e.g., less than 200° C.) or high (e.g., greater than 450° C.) temperatures. For example, coatings using organic particles or matrices may experience pyrolysis (i.e., decomposition) if exposed to temperatures above 200-300° C., and thus can not be used on glass that will be tempered after coating. On the other hand, most existing inorganic anti-glare coatings require high-temperature processing (e.g., greater than 450° C.) to obtain adequate curing.

BRIEF DESCRIPTION OF THE DRAWINGS

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The drawings are not to scale and the relative dimensions of various elements in the drawings are depicted schematically and not necessarily to scale.

The techniques of the present invention can readily be understood by considering the following detailed description in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a substrate;

FIG. 2 is a cross-sectional view of the substrate of FIG. 1 with an anti-glare coating formed thereon according to some embodiments of the present invention;

FIG. 3 is an isometric view of a particle within the anti-glare coating of

FIG. 2 according to some embodiments of the present invention;

FIG. 4 is a graph illustrating optical properties of various anti-glare coatings formed in accordance with some embodiments of the present invention; and

FIG. 5 is a flow chart of a method for forming an anti-glare coating, or for forming a coated article, such as an anti-glare panel, according to some embodiments.

DETAILED DESCRIPTION

A detailed description of one or more embodiments is provided below along with accompanying figures. The detailed description is provided in connection with such embodiments, but is not limited to any particular example. The scope is limited only by the claims and numerous alternatives, modifications, and equivalents are encompassed. Numerous specific details are set forth in the following description in order to provide a thorough understanding. These details are provided for the purpose of example and the described techniques may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the embodiments has not been described in detail to avoid unnecessarily obscuring the description.

The term “horizontal” as used herein will be understood to be defined as a plane parallel to the plane or surface of the substrate, regardless of the orientation of the substrate. The term “vertical” will refer to a direction perpendicular to the horizontal as previously defined. Terms such as “above”, “below”, “bottom”, “top”, “side” (e.g. sidewall), “higher”, “lower”, “upper”, “over”, and “under”, are defined with respect to the horizontal plane. The term “on” means there is direct contact between the elements. The term “above” will allow for intervening elements.

Embodiments described herein provide optical coatings, and methods for forming optical coatings, that improve the anti-glare performance of, for example, transparent substrates. In some embodiments, this is accomplished by using water-based suspensions of sheet-like particles, or “sheet particles,” in the optical coatings. The thickness of the sheet particles is relatively small compared to the length and width of the particles. The sheet particles form durable coatings in which the particles may be arranged in an irregular manner, resulting in porosity within the coating. In some embodiments, a hydrophilic silicone or silane emulsion, a hydrophilic silicone or silane solution, or a combination thereof is used as a binder, and in some embodiments, a surfactant as well.

The anti-glare coating may have an effective surface roughness between 0.2 and 5.0 micrometers (μm). The surface roughness and other properties of the coating may be influenced by processing parameters such as particle size, particle shape, loading, binder level, the addition of fillers, curing method, etc.

FIG. 1 illustrates a transparent substrate 100 according to some embodiments of the present invention. In some embodiments, the transparent substrate 100 is made of glass and has an upper surface 102 and a thickness 104 of, for example, between 0.1 and 2.0 centimeters (cm). Although only a portion of the substrate 100 is shown, it should be understood that the substrate 100 may have a width of, for example, between 5.0 cm and 2.0 meters (m). In some embodiments, the substrate 100 is made of a transparent polymer, such as polyethylene terephthalate (PET), poly(methyl methacrylate) (PMMA), polycarbonate (PC), and polyimide (PI). In some embodiments, an optical coating, as described below, is formed above the substrate 100 to create a coated article.

FIG. 2 illustrates a coated article (or anti-glare panel) 200. The coated article 200 includes the transparent substrate 100 and an anti-glare coating 202. The anti-glare coating 202 is formed above the upper surface 102 of the substrate 100 and includes sheet-shaped particles (or sheet particles or nano-sheets) 204, nano-particles 206, and a binder material (or binder) 208. The coating 202 has a thickness 210 of between about 1 and 100 μm. In some embodiments, an upper surface 212 of the coating 202 has a surface roughness of between 0.2 μm and 5.0 μm due to a series of surfaces formations formed thereon because of the presence of the sheet particles 204 and the nano-particles 206. It should be noted that in FIG. 2 the binder 208 may appear to substantially form the structure of the coating 202. However, the actual structure of the coating 202 may be substantially formed by the particles 204 and 206, which are held together, or in place, by the binder 208.

FIG. 3 illustrates one of the sheet particles 204, according to some embodiments, in greater detail. The sheet particle 204 is substantially plate-shaped and has, for example, a length 300 of between 300 and 500 nanometers (nm), a width 302 of between 150 and 250 nm, and a thickness 304 of less than 100 nm (e.g., less than 10 nm, such as between about 1 nm and 10 nm). It should be understood that the sheet particles 204 may vary in size. In some embodiments, the sheet particle(s) 204 is made of substantially pure silicon dioxide (i.e., no other materials may be present). In some embodiments in which the coating 202 is formed using a sol-gel system, the sheet particles 204 may be added via an aqueous solution/slurry, such as SUNLOVELY LFS HN-050 available from AGC Chemicals Americas, Inc., Exton, Pa. In some embodiments, the sheet particles are nano-clays, LAPONITE available from Southern Clay Products, Inc., Gonzales, Tex., or a combination of any of the previously-mentioned particles.

Referring again to FIG. 2, in some embodiments, the nano-particles 206 are spherical particles having a width of, for example, between 3 and 50 nm. The nano-particles 206 may be made of, for example, metals oxides, such as titanium oxide, silica, and fluorine-doped silica, metal fluorides, such as magnesium fluoride, and combinations thereof. Although shown in FIG. 2, it should be understood that in some embodiments, the nano-particles 206 are elongated, while in some embodiments, the nano-particles 206 are not included in the coating 202.

The sheet particles 204 are arranged in various ways within the anti-glare coating 202. For, example, some of the sheet particles 204 are essentially stacked in a “flat” manner, while others interact in such a way that irregular structures are formed, resulting in “pores” (i.e., spaces between the particles) being formed. For example, some of the sheet particles 204 may form relatively organized arrangements, similar to a “house of cards” due to differences between the surface charges at the edges and faces thereof, resulting in a large, regular porosity. The nano-particles 206 are dispersed throughout the coating 202, within the various spaces and/or pores formed between the sheet particles 204.

The sheet particles 204 have surface chemistries that are easily manipulated in aqueous systems to allow control over coating and gelation behavior, allowing them to produce dense conformal coatings or particles of aggregated nano-sheets without use of organic additives which require removal from the coating to produce a durable coating.

The anti-glare coating 202 may be deposited and/or formed using various methods. In some embodiments, the coating 202 is deposited on the transparent substrate 100 using a sol-gel system in which a sol-gel formulation is prepared and deposited onto the substrate 100 using, for example, spin coating, spray coating, slot-die coating, curtain coating, meniscus coating, dip coating, roller coating, draw down coating, or doctor blade coating. In some embodiments, the anti-glare coating 202 is applied directly to the upper surface 102 of the substrate 100. However, in other embodiments, other materials or layers may be formed between the substrate 100 and the anti-glare coating 202. Solvents in the formulation may be removed and/or the coating 202 may be cured using, for example, a thermal cure, a UV cure, or a combination thereof. In some embodiments utilizing a thermal cure, depending on the chemistry used, the coating 202 may be rapidly cured during tempering of the glass substrate (e.g., 650° C.-700° C.) or at lower temperatures (e.g., 100° C.-500° C.) when it is not desirable for the particular substrate to reach annealing temperatures.

In some embodiments, the sheet particles 204 (perhaps in combination with the nano-particles 206) are provided in a water-based suspension combined a hydrophilic silicone or silane emulsion, a hydrophilic silicone or silane solution, or a combination thereof, which is used as the binder 208, but may also serve as a surfactant. As will be appreciated by one skilled in the art, emulsions are two-phase mixtures of liquids in which the two liquids are usually immiscible, while solutions are single-phase mixtures of solutions. Examples of suitable binder materials include water-soluble dipodal reactive silanes, such as aminoalkoxysilanes, glycidoxyalkoxysilanes, carboxylalkoxysilanes, hydrophilic alkoxysilanes, and combinations thereof. These materials increase durability by increasing the adhesion and cohesion of the coating 202, while also decreasing the porosity of the coating 202. These materials also act as wetting agents and as effective binders for low and high temperature manufacturing processing, as the alkoxy groups form a thermally stable network through the sol-gel reaction, which also bond to the metal oxide nano-particles 206 and substrate 100. Catalysts, such as acids, bases, and metal carboxylates, may be used to enhance the rate of the sol-gel reaction.

Additionally, glycidoalkoxysilanes may also be cross-linked using the terminal epoxide (glycido) group, forming an organic polyether (epoxy) linkage, using suitable catalysts, such as ultra-violet (UV) catalysts, peroxides, and metal carboxylates. Further, glycidoalkoxysilanes may be cross-linked with dipodal alkoxysilanes that have a terminal amine or carboxyl group through the reaction between the epoxide and amine or carboxyl groups, requiring only modest heating to drive the reaction. Glycidoalkoxysilanes and aminoalkoxysilanes may also act as a coupling agent for forming strongly adhering coatings using these formulations on transparent polymer substrates. Such coatings may be cured at relatively low temperatures (e.g., less than 150° C.).

Aqueous solutions or emulsions of hydrophilic silicone surfactants may act as wetting agents during coating and convert into a silica binder when the coatings are heat treated above 300° C. in air or oxygen. They may not provide suitable binder properties until oxidized to silica, which may also be achieved using a UV-ozone treatment or an oxidizing plasma treatment. Hydrophilic silicones may also be used in conjunction with hydrophilic reactive silanes, in both low and high temperature processing methods.

Surface modification of the substrate 100 (e.g., a glass substrate) with a cationic (e.g. amine or ammonium) or an anionic (e.g. carboxylate) layer may be used to manipulate the structure of the interfacial layer by exploiting electrostatic effects between the charged surfaces of the particles and the substrate. Use of water as the primary solvent leads to significant cost savings when compared with organic solvents.

It should also be noted that UV curing options exist for binders containing alkoxy and/or glycido (epoxy) groups. UV curing may be used to selectively form organic network, siloxane network, or both by choice of UV photo-initiator. UV-curing may also be used in conjunction with lower temperature (e.g., less than 300° C.) thermal treatments (post-UV) to further promote formation of the siloxane network. UV-ozone or oxidizing plasma may be used to rapidly calcinate the binder into a pure silica binder at very low temperatures (e.g., less than 100° C.).

Using the methods described herein, dense anti-glare coatings may be provided, which do not require the use of toxic or environmentally hazardous during manufacturing. Anti-glare (light scattering) properties may be derived solely from the dispersed and aggregated sheet particles 204, perhaps in combination with the nano-particles 206. In some embodiments, larger particles (e.g., 0.1-2 μm) may also be used in the coating 202 to modify the anti-glare properties. The sheet particles 204 form extremely durable coatings due to the very high specific surface area and the high silanol (—Si—OH) density, which results in strong interfacial bonding between the sheet particles 204, the binder 208, and substrate 100.

FIG. 4 graphically depicts the haze and 60 degree gloss for various experimental anti-glare coatings formed in accordance with embodiments described herein. The anti-glare coatings were formed on 3.2 mm thick, solar float glass substrates using SUNLOVELY nano-sheet aqueous slurry, with 0%-0.10% SILWET L-77 hydrophilic silicone (available from Momentive Specialty Chemicals Inc., Columbus, Ohio) as wetting agent and sol stabilizer and binder. The coatings were processed at approximately 300° C. for about 10 minutes. Region 400 in FIG. 4 indicates desirable haze and gloss values for anti-glare coatings. As shown, at least some of the experimental coatings have these desirable properties. The embodiments described herein allow for precise control over important optical properties, which is beneficial because depending on the particular application, different combinations of haze-gloss may be desirable.

The sheet particle-based formulations exhibit improved durability over formulations based on submicron to micron scale light scattering particles due to greater interfacial area promoting improved cohesion and adhesion. Additionally, the durability of the anti-glare coatings described herein may be controlled by binder level, the addition of fillers, and method of curing. Additionally, the use of “green” aqueous formulation chemistry, including non-flammable and non-toxic materials, results in lower total manufacturing costs than traditional organic solvent-based formulations due to, for example, reduced solvent cost as well as reduced hazardous waste and material handling costs.

FIG. 5 illustrates a method 500 for forming an anti-glare coating, or for forming a coated article, such as an anti-glare panel, according to some embodiments. At step 502, the method 500 begins by providing a substrate, such as the transparent substrate 100 described above. At step 504, a coating formulation is applied to the substrate. The coating formulation includes an aqueous-based suspension of particles, such as those described above. At step 506, the coating formulation is cured (e.g., via thermal, UV, or a combination cure) to form an anti-glare coating above the substrate. At step 508, the method 500 ends.

Thus, in some embodiments, a method for coating an article is provided. A substrate is provided. A coating formulation is applied to the substrate. The coating formulation includes an aqueous-based suspension of particles. The particles have a sheet-like morphology and a thickness of less than about 100 nm. The coating formulation is cured to form an anti-glare coating above the substrate. The anti-glare coating has a thickness of between 1 μm and 100 μm.

In some embodiments, a method for coating an article is provided. A transparent substrate is provided. A coating formulation is applied to the transparent substrate. The coating formulation includes an aqueous-based suspension of particles and a hydrophilic silicone or silane emulsion, a hydrophilic silicone or silane solution, or a combination thereof. The particles have a sheet-like morphology and a thickness of less than about 100 nm. The coating formulation is cured to form an anti-glare coating above the transparent substrate. The anti-glare coating has a thickness of between 1 μm and 100 μm.

In some embodiments, a coated article is provided. The coated article includes a substrate and a coating formed above the substrate. The coating includes an aqueous-based suspension of particles and has a thickness of between 1 μm and 100 μm. The particles have a sheet-like morphology and a thickness of less than about 100 nm.

Although the foregoing examples have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed examples are illustrative and not restrictive. 

What is claimed:
 1. A method for coating an article, the method comprising: providing a substrate; applying a coating formulation to the substrate, the coating formulation comprising an aqueous-based suspension of particles, wherein the particles have a sheet-like morphology and a thickness of less than about 100 nanometers (nm); and curing the coating formulation to form an anti-glare coating above the substrate, the anti-glare coating having a thickness of between 1 micrometer (μm) and 100 μm.
 2. The method of claim 1, wherein the coating formulation further comprises a hydrophilic silicone or silane emulsion, a hydrophilic silicone or silane solution, or a combination thereof.
 3. The method of claim 1, wherein the particles comprise silicon oxide.
 4. The method of claim 1, wherein the coating formulation further comprises a plurality of nano-particles.
 5. The method of claim 4, wherein each of the nano-particles has a width of between about 3 and 50 nm.
 6. The method of claim 5, wherein each of the nano-particles are made of a metal oxide.
 7. The method of claim 1, wherein the coating formulation comprises a silane emulsion, and wherein the silane emulsion comprises an aminoalkoxysilane, a glycidoxyalkoxysilane, a carboxylalkoxysilane, a water soluble silicate, a hydrophilic alkoxysilane, or a combination thereof.
 8. The method of claim 5, wherein the curing the coating formulation comprises an ultraviolet (UV) cure, a thermal cure, or a combination thereof.
 9. The method of claim 1, wherein the coating formulation is a sol-gel formulation.
 10. The method of claim 1, wherein the substrate comprises glass.
 11. A method for coating an article, the method comprising: providing a transparent substrate; applying a coating formulation to the transparent substrate, the coating formulation comprising an aqueous-based suspension of particles and a hydrophilic silicone or silane emulsion, a hydrophilic silicone or silane solution, or a combination thereof, wherein the particles have a sheet-like morphology and a thickness that is less than about 100 nanometers (nm); and curing the coating formulation to form an coating above the transparent substrate, the coating having a thickness of between 1 micrometer (μm) and 100 μm.
 12. The method of claim 11, wherein the particles comprise silicon oxide.
 13. The method of claim 12, wherein the coating formulation further comprises a plurality of nano-particles, wherein each of the nano-particles has a width of between about 3 and 50 nm.
 14. The method of claim 13, wherein the curing the coating formulation comprises an ultraviolet (UV) cure, a thermal cure, or a combination thereof.
 15. The method of claim 14, wherein the coating formulation is a sol-gel formulation.
 16. A coated article comprising: a substrate; and a coating formed above the substrate, the coating comprising an aqueous-based suspension of particles and having a thickness of between 1 micrometer (μm) and 100 μm, wherein the particles have a sheet-like morphology and a thickness of less than about 100 nanometers (nm).
 17. The coated article of claim 16, wherein the coating further comprises at least one of a hydrophilic silicone, water soluble silicate or silane emulsion a hydrophilic silicone or silane emulsion, a hydrophilic silicone or silane solution, or a combination thereof.
 18. The coated article of claim 17, wherein the coating comprises a silane emulsion, and wherein the silane emulsion comprises an aminoalkoxysilane, a glycidoxyalkoxysilane, a carboxylalkoxysilane, a water soluble silicate, a hydrophilic alkoxysilane, or a combination thereof.
 19. The coated article of claim 18, wherein the coating further comprises a plurality of nano-particles, wherein each of nano-particles has a width of between about 3 and 50 nm.
 20. The coated article of claim 16, wherein each of the particles comprises silicon oxide. 